This invention relates generally to means enabling a ceramic article to be provided with an adherent organic polymer lubricating film which resists mechanical wear of the coated article at elevated temperatures up to 500.degree. C. and higher, and more particularly, to affording such protection to a variety of ceramic articles including both crystalline and vitreous ceramics.
Lubrication is a well recognized means to reduce friction and wear between surfaces in dynamic contact. Two major areas for which improved lubricants are needed for continued progress are metal forming and transportation. Better metal forming capabilities to minimize machining and grinding require lubrication techniques and lubricants that can be used effectively at temperatures approaching the melting points of the metals now employed. In transportation, one of the most productive areas for increasing energy efficiencies is often referred to as the "adiabatic" engine wherein temperatures range from 500.degree. C. and 1100.degree. C. making the selection of lubricants and means of lubrication still difficult. A known technique for lubricating at such temperatures is the use of solid lubricants in the form of plasma sprayed coatings of the metals and ceramics being employed. More recent developments whereby an adherent solid polymeric lubricating film is deposited on a ferrous metal surface to afford such protection are reported in technical publications entitled "In Situ Formation of Solid Lubricating Film from Conventional Mineral Oil and Ester Solid Duda, E. E. Graham and E. E. Klaus, ASLE Proceedings, 3rd International Conference on Solid Lubrication, ASLE SP-14 1984 and "Lubrication from the Vapor Phase at High Temperatures", authored by E. E. Graham and E. E. Klaus, ASLE transactions volume 29, no. 2, pages 229-234 (1986). As described in said technical publications, the metal surfaces are deemed to have a catalytic effect upon the vapor phase reactants whereby surface polymerization of said reactants takes place to produce the protective film. Possibly the absence of comparable metal catalytic agents in ceramic materials has prevented the formation of the protective film in such manner. More particularly, a vapor phase deposition of the same reactants under the same process conditions has thus far only produced non-adherent surface deposits affording no substantial protection to the underlying ceramic substrate.
Silicon carbide and silicon nitride ceramics are now being studied extensively for high temperature engineering applications as above indicated, to include advanced heat engines and gas turbines. Both ceramics are crystalline materials with silicon carbide being a very hard material which is both corrosion and thermal resistant, is lighter than steel and exhibits a high thermal conductivity and low thermal expansion whereas silicon nitride is characterized by low thermal expansion, excellent corrosion resistance and high temperature stability. On the other hand, both of said ceramic materials undergo significant mechanical abrasion when subjected to the dynamic wear conditions being experienced with such product applications. Vitreous silica or fused quartz represents still a different type ceramic material experiencing aggravated physical wear if subjected to dynamic conditions at elevated temperatures. Accordingly, it remains desirable to produce an effective means enabling various products formed with either crystalline or vitreous ceramic materials to be provided with a protective coating resistant to dynamic wear conditions such as abrasion and adhesive wear up to elevated temperatures of at least 500.degree. C.
It is one object of the present invention, therefore, to provide effective means whereby an adherent lubricating film can be deposited on various ceramic substrates affording resistance to mechanical wear of the coated article at elevated temperatures up to at least 500.degree. C.
It is another object of the invention to provide novel surface treatment means enabling a treated ceramic surface to be thereafter provided with an adherent wear resistant coating.
Still another object of the present invention is to provide a novel method for surface treatment of the ceramic article so as to enable subsequent deposition of a wear resistant protective coating on the treated ceramic surface.
A still further object of the present invention is to provide a novel method enabling a wear resistant protective coating to be formed on a ceramic article
These and still further objects of the present invention will become apparent upon considering the following detailed description of the present invention.